The invention relates to a wheel force measuring hub assembly with an exterior ring part attachable to a wheel rim, an interior ring part attachable to a vehicle axle, measuring webs connecting the ring parts and strain gauges on the measuring webs.
In German Patent Document DE-OS 2302540, an assembly is described which has an exterior ring part, an interior ring part and four measuring webs which connect both ring parts with one another and are each angularly offset by 90.degree. with respect to one another. On the measuring webs, strain gauges are arranged in order to be able to detect the forces acting upon the wheel.
From German Patent Document DE-OS 3213319 an assembly is also known which has a central hub part, a rigid, ring-shaped rim part and four spoke parts. The four spoke parts extend from the hub part at a right angle with respect to one another radially to the outside and each have a rectangular cross-section. In addition, four chord parts are provided which, in the center, are connected with the exterior ends of corresponding spoke parts and are connected with their two ends with respective rim parts. For measuring the forces acting upon the assembly, strain gauges are provided on the four spoke parts and--connected in corresponding bridge circuits--supply the corresponding signals for the individual forces and torques to be determined.
However, by means of the respective wheel force measuring assemblies described in the above-mentioned published patent applications, it is not possible to satisfactorily, separately and uninfluenced from one another and with the exclusion of external environmental influences, measure the forces and torques to be determined, specifically the longitudinal force of the wheel Fx, the wheel contact force Fz, the lateral force of the wheel Fy, the camber torque Mx, the return torque Mz, and the braking torque My.
It is an object of the invention to further develop a wheel force measuring assembly of the initially mentioned type such that the forces and torques to be determined can be precisely determined without influencing one another. Also, the rotational wheel speed should be determined in a high-resolution manner.
This and other objects are achieved by preferred embodiments of the present invention wherein said strain gauges are configured such that substantially all wheel forces are determined by way of shearing strains on said strain gauges.
Accordingly, in the case of a wheel force indicator of the initially mentioned type, the strain gauges are arranged, aligned and connected with one another on the measuring webs such that all forces and torques can be determined exclusively by way of the shearing strain occurring during the loading. By means of this measure, it is possible to optimally decouple the individual force and torque components from one another and to sense them separately. The advantage of this measuring method will be explained in the following.
According to a preferred embodiment of the invention, openings or oblong holes are arranged in the area of the transition between the measuring webs and the exterior ring part. Beyond the above-mentioned measure, this permits a still better decoupling of the corresponding forces and torques so that only one type of forces and torques is introduced into the individual measuring webs, whether they are aligned perpendicularly with respect to or in the driving direction. In this case, the dimensioning of the openings or oblong holes preferably takes place such that the separation of forces and torques as well as a considerable increase of the measuring sensitivity is achieved in an optimal manner.
According to a preferred embodiment of the invention, a signal processing, transmitting and analyzing device is provided which transmits the data obtained by means of the strain gauges during a measuring operation from the rotating wheel force measuring hub assembly to a part fixed to the vehicle.
A radio transmission can also be used for this purpose. As an alternative, the transmission can be carried out by means of an infrared telemetry transmission device. This makes it possible to transmit the plurality of the occurring data rapidly and without errors from the rotating hub assembly to a corresponding measuring data sensing device in the vehicle.
For analyzing the corresponding signals of the strain gauges on the measuring webs, it is required to precisely know the position of the wheel on the vehicle or of the measuring value generator so that it can be indicated whether the measuring webs are aligned perpendicularly to or in the driving direction. For this purpose, preferably at least one Hall sensor is provided which interacts with a pulse ring connected with the measuring-value sensor. An electronic control unit can analyze the data supplied by the Hall sensor and a conclusion can be drawn therefrom on the position of the measuring hub assembly. The pulse ring can be fastened, for example, on the exterior ring part of the hub assembly. The Hall sensor is fixedly arranged on the vehicle. As an alternative, other angle position sensing devices can also be used.
According to a preferred embodiment of the invention, two Hall sensors are provided which are angularly offset with respect to one another such that a rotating direction sensing is permitted. As a result, not only the absolute position of the wheel indicator and, by the encoding of the pulse ring, the 0.degree.-angle of the measuring system can be easily determined as well as also the rotating direction.
A control arrangement can also be accommodated in the interior ring part so that already analyzed data can be transmitted by way of a transmission device to another control and analysis unit in the vehicle. The transmitted measuring signals can be used for the development and control of driving dynamics control systems.
According to especially preferred embodiments the strain gauges which sense only shearing strains are arranged in a special manner for being able to appropriately sense the forces and torques to be determined. In particular, arranging possibilities are also indicated for connecting the strain gauges with one another to full bridge circuits so that a particularly well resolving and precise measuring arrangement is ensured. The corresponding advantages and characteristics are therefore further described in the following.
It is also an advantage for the strain gauges on the measuring webs to be covered, for example, by means of a casing of the measuring webs so that environmental influences (such as the radiation heat in the surrounding field of the torque indicator during a braking operation) can have no effect on the measuring results. Nevertheless, care should be taken that the cooling is sufficient.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.